PSI - Issue 81

Mykola Riabchykov et al. / Procedia Structural Integrity 81 (2026) 367–371

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The main properties of the obtained mixture (Fe ₃ O ₄ , Fe² ⁺ /Fe³ ⁺ composite) can be summarized as follows. Magnetic properties – the particles are attracted to a magnet; their properties depend on particle size. The structure of the mixture can be described as an inverse spinel. The density is approximately 5.17 g·cm ⁻ ³. The mixture is insoluble in water but dissolves in hydrochloric or sulfuric acids with the formation of Fe² ⁺ /Fe³ ⁺ ions. The substance is stable in th e absence of oxygen; upon exposure to oxygen, it oxidizes to γ -Fe ₂ O ₃ . The substance contains hydroxyl groups ( – OH), which are useful for functionalization (binding organic molecules, polymers). The obtained substance was applied to the surface of textile fibers according to the following procedure. First, cleaning was carried out – washing in a neutral detergent solution to remove fats, waxes, and sizing agents. For natural fibers, additional treatment with a NaOH solution (mercerization) was performed. The resulting magnetite precipitate was dispersed in an aqueous-alcohol medium with stabilizers. The suspension concentration was typically 1 – 10 g/L. The main coating method used was pad-dry. In this process, the textile was immersed in the dispersion, squeezed to the required wet pickup (70 – 100%), and dried at 80 –100 °C. Thermofixation was carried out in a drying oven at 120–160 °C (for synthetics – below the melting point). 3. Main results The modified fibers acquired a darker color, along with magnetic properties. Microscopic analysis showed a predominant localization of particles in the cavities and on the fiber surface (Fig. 2). The images demonstrate the presence of quite pronounced clusters of components added to the fibers. Along with the uniform application of magnetite to the fiber surface, inclined dark stripes are observed. These stripes determine the increased density of the powder on the fiber surface. It should be noted that traditionally textile fibers have certain irregularities in the form of grooves and protrusions located around the circumference of the fiber. Such depressions form a system of concentrators that significantly reduce the potential strength of the fiber. Fig. 2 proves that the developed technology allows filling these irregularities with structures whose microstrength is higher than this indicator for the fiber material. The effect of added magnetite can be dual in nature. The first determines the application of a stronger material to the fiber surface. This strong material also fills the microirregularities on the fiber surface.

Fig. 2. Textile fiber coated with magnetite.

The incorporation of a nanomagnetic mixture into textile fibers fills potential stress concentrators, thereby increasing their strength. The stress – strain state of the fibers was analyzed using finite element analysis with both two-dimensional and three dimensional elements, following the approach described by Riabchykov et al. (2018). A fiber model with natural stress concentrators was subjected to longitudinal loading. The scales located on the fiber surface generate additional stress sources, resulting in elevated internal stresses within the fiber (Fig. 3a). When the mixture of divalent and trivalent iron oxides is applied to the fiber surface, it accumulates in the cavities between the scales, reducing stress concentrations. Consequently, the internal stress level within the fiber is substantially decreased (Fig. 3b). After conducting a series of experiments to determine the tensile strength of textile fibers, these results were confirmed. A single-yarn tensile strength tester Y001A was used. The specific tensile strength of fibers was determined per unit cross-sectional area.